Catalytic activity of supported heteropoly acids for reactions requiring strong acid centres

The effect of supports such as silica, alumina, amorphous aluminosilicate and magnesia on the activity of heteropoly acids (HPA) for reactions requiring strong and very strong acid sites has been studied. It has been found that 12-tungstophosphoric acid (HPW) mounted on alumina and silica catalyses cumene cracking at 150 °C, with conversion ca. 90%, and toluene disproportionation at temperatures as low as 250 °C. The catalytic performance increased with increasing HPA content and reached its maximum in the loading range 38–50 wt.%. With > 38 wt.% HPW on silica and > 60 wt.% HPW on γ-alumina the supported HPW catalysts showed catalytic activity for low-temperature isomerisation of hexane as did unsupported HPW. Activity for the latter reaction indicates the presence of very strong acid centres with acid strength approaching that of superacids. No activity for the reactions studied was found for magnesia-supported HPW.